[MrPedantic]

Hello Word

1. I would like Alice, Tom, Dick, and Harry to do X.
2. I would like Alice, Tom, Dick and Harry to do X.

The extra comma in #1 is called the "serial" or "Oxford" comma (because it occurs in "series", and because it's favoured by the Oxford University Press). Till about 60 years ago, you would almost always find the serial comma in a list of this kind.

In the UK, it has largely fallen out of favour; you rarely see it in business correspondence, magazines, newspapers, etc. But it does still survive in the book trade, especially in publishing houses such as OUP, Penguin, etc.

I'm not so sure about US usage, though I do tend to see the serial comma in US academic publications, etc. (but not so often in newspapers and magazines). To judge by website usage, US users are more likely to use the serial comma than British users.

If you google on "serial comma", you can find much heated discussion on the subject. Sometimes the extra comma is necessary to avoid ambiguity; but on the whole, it seems to be a question of personal preference.

All the best,

MrP

PS: I like the screen name. I'm surprised no one had thought of that one.